From the prior art it is known to use interlocking or claw-type shifting elements in automatic transmissions, whereby drag torques are advantageously largely avoided. Furthermore, by virtue of their interlocking transfer mode, claw shifting elements need lower actuating forces and take up less structural space than disk shifting elements. As a rule, those shifting elements are made as interlocking shifting elements which are only disengaged during upshifts, or which are engaged as shifting elements only in the reversing gear.
In automatic transmissions with frictional shifting elements it is known from the prior art to control the system pressure separately from control systems for shifting elements and other, special control processes as a function of the transmission capacity of the shifting elements in the gear concerned, such that in the case of other control processes of shifting elements and components of the transmission the system pressure is controlled, as a function of the requirements during the other control processes, by the specification of a minimum or maximum pressure.
During shifts or gear engagement processes the system pressure is controlled as a function of the transmission capacity of the shifting elements in the condition before the shift or gear engagement and the transmission capacity of the shifting elements in the condition after a completed shift or after a completed gear engagement and as a function of a minimum pressure specification, in order to enable a sufficient pressure for filling the shifting elements. From these pressure fractions, by way of a maximum selection that pressure is calculated, which is produced during shifts or gear engagement processes.
Particularly in automatic transmissions with interlocking shifting elements, when disengaging or engaging the shifting elements it is necessary to enable a system pressure control which, while the lateral force on the interlock of the shifting elements has not been eliminated completely, provides an increased force in the respective engagement or disengagement direction.
DE 10 2008 001 196 A1 by the present applicant describes a hydraulically or pneumatically actuated interlocking shifting element comprising a hydraulically or pneumatically actuated piston having a piston space containing the hydraulic or pressure medium, a pressure medium inlet for the piston, a claw, and a counter-claw with which the claw engages in the engaged condition. In this known shifting element it is provided that the engagement speed of the claw in the event of a tooth-on-tooth position of the claws relative to one another is increased by decoupling the claws from the hydraulic or pneumatic volume flow and by prestressing the claw by means of a hydraulic or pneumatic pressure reservoir which is functionally connected to the piston and connected to the pressure medium inlet line.